Phase Equilibria in the Quasibinary Li₂O⋅2B₂O₃–Yb₂O₃⋅B₂O₃ System, Assessment of Stability, and Conductivity of Solid Solutions Based on Li₂O⋅2B₂O₃

Abstract

Using the methods of differential thermal analysis and X-ray powder diffraction, the Т–х phase diagram of the Li₂O⋅2B₂O₃–Yb₂O₃⋅B₂O₃ system has been constructed. Phase diagram of this system belongs to the eutectic type and is characterized by the formation of limited Li₂O⋅2B₂O₃–based solid solutions. The region of limited (1 – х)Li₂O⋅B₂O₃–хYb₂O₃⋅B₂O₃ solid solutions at 298–1038 K is x = 0–0.1 mole fraction of Yb₂O₃⋅B₂O₃ (or α-Li₂O⋅2B₂O₃). Eutectic coordinates: 1038 K and ~17 mol % Yb₂O₃⋅B₂O₃. Depending on the thermal history, (1 – х)Li₂O⋅2B₂O₃–хYb₂O₃⋅B₂O₃ (x = 0–0.1) solid solutions are formed both in the form of polycrystals (annealed) and in the form of amorphous glasses (quenched). Glassy and polycrystalline samples of solid solutions α-Li₂O⋅2B₂O₃ (x = 0, 0.05, and 0.1) were synthesized and their physico-chemical properties were studied. The temperature dependence of the standard Gibbs energy of the reaction of formation of solid solutions is estimated (0 ≤ х ≤ 0.1 at 573–1073 K). It is shown that the formation reaction of a solid solution based on Li₂O⋅2B₂O₃ in the range 0 ≤ х ≤ 0.1 mole fraction Yb₂O₃⋅B₂O₃ is thermodynamically possible under standard conditions. Measured the electrical properties of (1 – х)Li₂O⋅2B₂O₃–хYb₂O₃⋅B₂O₃ (x = 0, 0.05, 0.1) glass samples solid solutions (x = 0–0.1) in the temperature range from 298 to 575 K. The temperature dependences of the direct current (dc) conductivity of α-Li₂O⋅2B₂O₃–samples with different thermal histories (annealing or quenching) differ from each other. It was shown that the introduction of Yb₂O₃⋅B₂O₃ (x = 0–0.1) into (1 – х)Li₂O⋅2B₂O₃–хYb₂O₃⋅B₂O₃ glasses reduces the conductivity of the samples. The activation energies of conductivity of the glass samples are determined (66.6–90.7 kJ/mol). At temperatures >575 K, the conductivity of α-Li₂O⋅2B₂O₃ glasses deviates from the Arrhenius equation.